After he assailed Oprah Winfrey's couch in May 2005, you have to hope Tom Cruise mused on the meaning of change. When he imagined his outbreak of zaniness, maybe it played in his head like a bar scene from Cocktail; but the derision with which the public greeted it was a tiny hint that the mood toward movie stars had darkened since Cruise's jubilant 80s and 90s. Hollywood's reigning king of kings was sacked by Paramount 14 months later, and though he was later made head of the revitalised United Artists, he's not in the clear yet: the knives are already out for his much-delayed Hitler assassination pic, Valkyrie.

Dark clouds have gathered over the whole of Hollywood's top tier. "Star power is definitely waning," says one producer at a major Hollywood production company. "There's no mystique any more. The power of celebrity has been commodified, and that weakens people's willingness to go and see stars. I can see Tom Cruise on Perez Hilton; why should I go to the cinema?"

The showbiz colossi that straddled the industry in top-heavy, high-concept blockbusters are fading: Arnold gone to politics; Mel gone off the rails; Bruce, Sly and Harrison all making their last throw of the dice with the recent returns of their superannuated franchises. Other stars have followed in their wake, of course, but few with the power to carry a movie. Will Smith is the only actor widely regarded as a sure thing at the box office, transcending race, class and even, as this month's Hancock showed, duff reviews.

You can't exactly say the stars got small, but somewhere along the line, in the 90s, it was the pictures that got big. The huge franchises that now dominate the release schedules, rolled out like military operations, often employ ensemble casts and invariably splurge on the CGI, decentralising the importance of the star actor. The Sparta epic 300 was typical of new-millennium thinking: jacked up to the helmet plumes on comic-book attitude and blue-screen aesthetics, but not a big-name actor in sight.

In this climate, the studios are beginning to seriously question whether the A-list are worth the going rate. Going or gone are the deals that were routine a few years ago, whereby a star would receive a fixed fee plus a percentage of the eventual box-office haul (Keanu Reeves tops the earning charts, having bagged $30m plus 15% to make an eventual $256m from the Matrix sequels). With the DVD profits that made these deals possible shrinking, and the world economy on the turn, Hollywood is looking to tighten its belt.

And in an industry awash with projects, it's harder to locate meaningful roles that reflect our inner desires - the roles that are the genesis of stardom. "There's just more product," says the producer, "and that didn't used to be the case. It's got to be harder for agents and managers to build [star careers] - you've got to get through the clutter." Everyone feels the change coming. The rumour in Hollywood is that the studios will use the ongoing negotiations with the actors' unions to clamp down on deals that indulged star muscle. It's no coincidence that a lot of big hitters have been shifting between the talent agencies this year (next big thing Ellen Page, of Juno, was one of the most recent defections). The stars are nervous.

But it was the stars themselves who set the ball rolling six decades ago. Olivia de Havilland was the groundbreaker: unhappy with the roles she was offered, she contested her contract with Warner Bros. It was a break for freedom that would help bring down the studios, and start to sever the rope that binds the audience and the admired. Prior to this, Hollywood moguls had totally controlled their stables of actors, paying them a fixed weekly wage and road-testing them in a variety of roles until they found a "type" that chimed with the public. In what's been called "the industrialisation of the ineffable", Hollywood became a streamlined machine for nosing out the qualities that made certain actors strike a chord with the public.

But the stars, for all the exaltation, often felt trapped by these creations. De Havilland successfully freed herself in 1945; the rest of the thoroughbred performers found themselves unshackled when the studio system collapsed completely in 1948. People such as Tyrone Power Jr, chained to his stipulated pretty-boy designation for years, suddenly found themselves able to explore roles not permitted by the studio machine - something Brad Pitt, a modern counterpart fond of wandering into indie roles, takes for granted. The elite were suddenly in charge of their own image and destiny. The modern star system was born.

You could call Clint Eastwood the paradigm of postwar stardom. A 40-year phenomenon, he used his liberated status to become a massively successful actor-producer-director who blazed the trail for roving renaissance men such as George Clooney. And the role that made him a star, in Sergio Leone's A Fistful of Dollars, was vital. A lone gun out for the pickings, he was a perfect fit for Hollywood's new freelance stars. But even more, he was the incarnation of an audience for whom certainties and values had been eroded by the second world war and, in America, the gathering storm of Vietnam.

Deference is no longer in the picture in terms of how people consume films, either. Bill Quigley, chairman of the Quigley Publishing Company, which publishes an annual survey of the top 10 money-making stars, says: "What's fascinating to me is that box office is a spectator sport now - people are totally obsessed with films' performance, at least in the States." Increasingly, the puppet-masters - directors - became stars in their own right, especially after the rush of auteur worship in Hollywood in the 70s.

In fact, the power in the movies now lies not with studios or stars, but with consumers. Stars may have greater freedom to choose their projects, flitting between Hollywood and the independents, but they've lost the solid, eager constituencies of their studio forebears. The public is more fickle in a marketplace heaving with alternatives, and it's harder for stars to connect with those who watch them. What is apparent is not just the weakening echo of familiar names, but the lack of conviction in new faces. There seems to be a particular problem finding new male stars: Colin Farrell and Jude Law, whose six-movie push at the end of 2004 went nowhere, are two high-profile misfires. Johnny Depp's promotion from Tim Burton kooksville to major actor has been the most notable recent rise, but doubts remain about his bankability outside the Pirates franchise; it remains to be seen if the similarly leftfield Robert Downey Jr can thrive as a marquee name away from Iron Man.

Although female stars arguably retain more star-power than the men, one of them also exemplifies the pressures on the notion of the movie star. Angelina Jolie is a household name - if not yet trusted to open a movie - but less for her films than for her tattoos, her children, her love life and the air of chaos that has often attended her. Seeing how Jolie - and other actors - are treated by public and press alike must lead many young actors to wonder, "Is that level of fame worth the cost?"

The internet has accelerated the process of turning actors into so much meat for the celebrity mincer, intensifying the volume of gossip to the point where the gentlemanly consensual fantasy that underpinned studio stardom - that the persona an actor showed on screen was somehow "the truth" - has been yanked inside out. The real-life gonzo narratives created by the media often seem more important: "Lindsay Lohan" rings out far louder from the web than any of her films. Mark Borkowski, the PR veteran and author of The Fame Formula, compares it to another mass-communication revolution: the advent of radio in the 20s, when the sudden ability to hear people talking for themselves shattered the air of privilege surrounding the silent stars. That change entailed the creation of dedicated publicity departments by the studios, and a similar adjustment may be overdue in today's digital world. "It's nowhere near any sense of maturity at all," Borkowski says.

In the digitised world, the distance between stars and audience is shrinking faster than ever, and the foundations of fame are undergoing a tectonic shift. People want the personalised treatment: entertainment that is "one to one", not the traditional "one to many" model of cinema, ultimately pushing to be the stars of their own narratives. They are enshrining their lives on Facebook and MySpace, creating avatars on World of Warcraft and Second Life, and are back in cinemas, leaning forward into the frame with the return of 3D. It is time for Me.plc, as Borkowski puts it; ultimately, it is us conspiring to kill the stars.

A sense of unease is building within the film industry. "It ain't like we ain't trying," says the Hollywood producer. "We're trying to create aspirational heroes, ass-kickers. The Gladiator moments. People still want that, and we have to deliver, but they're becoming more empowered to create something for themselves." Borkowski says the stars can adjust to this seismic shift, if they take up the weapons of the new age - blogging, astroturfing (a PR campaign seeking to fake grassroots enthusiasm), communicating their persona at eye level. Such an effort could, he believes, be liberating: "You're not dependent on whether your agent likes you or not. But without them, you have to have compelling content. You have to have a point of view."

In order to survive, the stars have to grasp this demotic drive, otherwise they may only exist in diminished form. But are they truly interested? Rock luminaries instinctively understand the power of intimacy - Kanye West is one who has caught the eye with his blogging - but there is something fundamentally aloof about Hollywood. Borkowski commends only a shrewd few who are adapting well: JJ Abrams and his canny faux-YouTube marketing ("I'm not sure he succeeds, but he gets the atmosphere right"); Juno director Jason Reitman for his sassy attitude, as demonstrated on his MySpace page ("He'll suck the dick of the studio, but he's not party to it"); Leonardo DiCaprio, for his political stance; and Bourne star Matt Damon, who according to Forbes is Hollywood's best-value performer in terms of profit against his fees. Borkowski mentions Damon's lobbying to get Paul Greengrass on board the Bourne franchise, a key decision in dragging the films towards the jittery aesthetics that later infiltrated the new-look Bond. But two of the subjects of Borkowski's praise are not actors, and the other two were established names already.

No matter what reality TV tells us, we can't all be stars; the stars' job is to recapture the high ground and remind us of the meaning of exceptional. They may have plenty of time to ponder this - until Hollywood restores compelling human narrative alongside spectacle in its priority list, in fact. Meanwhile, maybe Damon truly is the icon for the times: nondescript, utilitarian, fit for purpose. Perfect for a decade that has been defined by living under threat. The A-list might have to accept being harried, frowning, unshaven, out of focus for a while - at least until we start dreaming about the possibility of a better world, and of glamorous beings, again. Where we go, the stars must follow; that's the secret Hollywood's golden ones have been keeping all these years.